A method is provided of application protocol monitoring for a manufacturing line including the steps of constructing a manufacturing line model for the manufacturing line, utilizing logic for a programmable logic controller (PLC), executing a control logic simulation of the PLC logic to validate the PLC logic against the manufacturing line model, creating a database containing validated I/O tag expected intents confirmed from the control logic simulation, and applying the application protocol monitoring device to a network for the manufacturing line to monitor traffic across the network and continuously compare the I/O tag status across the network to the database of validated I/O tag expected intents.